Theoretically if you are running x64 Windows then you can run an x64 (i.e. amd64) VM. However it will depend on whether you have virtual extensions enabled in the host BIOS (i.e. supports allowing the full CPU options through to the VM). Also it will depend on the VM platform that you use - you may need to tweak some settings somewhere...

If you are ok with the 32 bit version (i.e. i686) then no worries, but if you want to try to run the 64 bit version then I suggest you see if your VM platform provider has some support mechanism (such as forums, mailing list or even a wiki) to assist you configuring your host to support 64 bit guests.

ehm.. it seems like VM has problems with x64, or x64 was not configured in VM profile.

technically, if not speaking about VTx differences and some multimedia extensions, AMD and Intel x64 are the same. So, you can even disable VTx and still run the code on VBOX or VMWare (with disabled vtx option, of course).